RFID tags are used to track items such as inventory. The tracking process involves sending an RF signal to the tag and receiving a response signal at a tag reader. The tag reader receives a serial number or other information from the tag and stores the received data. Problems can occur when many tags are within range of the reader and their responses interfere with each other or when signals are attenuated by distance or interference. Further, the RF energy required to read a tag must be strong enough for the tag to generate the response signal. This limits the range at which RFID tags can be used.